Storage experts: Does size matter?

Hard drives, large and small

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You The Expert There has been much ado about 2.5-inch, small form-factor (SFF) hard disk drives of late and how they are better than the larger 3.5-inch drives. Does size matter?

Several storage array vendors have started using SFF drives in their arrays. The VSP from Hitachi Data Systems is one such drive. HP has OEMed this from HDS's parent Hitachi as its P9500. IBM's Storwise V7000 and DS8800 arrays are also SFF fans. NetApp has adopted 2.5-inch drives in its latest FAS arrays, and Compellent has added extra support for SFF drives in it latest Storage Center array.

Are SFF drives really better than 3.5-inch drives? For sure, SFF drives need less power to spin and there can be more of them in a drive tray meaning you can spread data across more spindles and get better I/O rates. But drives are mechanical and they break. So the more there are in an enclosure or rack the greater the probability of a drive failing and its data needing recovery or re-building.

Also the increased I/O you get from more spindles is a small improvement compared to the much faster I/O you can obtain from solid state drives (SSDs) which, since they are solid state and not mechanical, are less prone to error and failure.

SSDs are more expensive gigabyte for gigabyte, so SFF drives can provide a better balance of affordability, capacity and performance. Perhaps the ideal array at present is one with SSDs for the small core of hot data, SFF drives for less highly active data which is present in larger amounts, and traditional 3.5-inch drives for storing the bulk data which has low access rates but still does need to be directly online.

A countervailing view is that multi-level cell flash holds more data for less money than the faster single-level cell flash. This would mean therefore, that you only need two tiers of storage in an array – SSD and traditional 3.5-inch drives – with no place for the 2.5-inch drives and no need for them. They are a stopgap, that's all.

Does size matter? We have asked some reader-experts what they think about the issue and we'll publish their thoughts on low-power and small versus larger, higher capacity drives later this week. ®